Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.89   11.160%   $94.3637   $94.36   $94.35   $94.40  
  Purchase #2 $236.96   9.509%   $259.4925   $259.49   $259.50   $259.50  
  Purchase #3 $154.42   8.421%   $167.4237   $167.42   $167.40   $167.40  
  Purchase #4 $114.98   10.390%   $126.9264   $126.93   $126.95   $126.90  
  Purchase #5 $81.79   7.562%   $87.975   $87.98   $88.00   $88.00  
  Purchase #6 $138.73   10.723%   $153.606   $153.61   $153.60   $153.60  
  Purchase #7 $10.56   7.682%   $11.3712   $11.37   $11.35   $11.40  
  7 purchase totals = $822.33       $901.1585   $901.16   $901.15   $901.20